Ok, It's time for a physics problem.
Q: A 200 (91Kg) pound runner is running at 7 Mph (3.3 m/s) before he collides with a 2 year old child whose moron negligent parent isn't watching them while they wander around the track, where they shouldn't be anyway...
How much force is absorbed by the child when he darts out in front of the runner?
F = m * a
F= 91Kg * 3.3 m/s
Force required to fracture a skull: Variable, but as little as 73N.
So, here's my point... DO NOT let your toddlers play on a track. You might as well let them play in traffic! If they dart out and chase a ball under a runners feet, they could seriously die.